Changes In Posterior Elevation Research Articles

Correlation between the ablation ratio and posterior corneal stability after small incision lenticule extraction for high myopia

PurposeThe aim of this study is to investigate changes in posterior corneal elevation and their correlations with the ablation ratio 3 years after small incision lenticule extraction (SMILE) for high myopia.MethodsEighty eyes underwent SMILE were enrolled in this study. Eyes were classified into two groups based on the ablation ratio (AR, lenticule thickness from SMILE machine/thinnest corneal thickness): group A (< 25%, 40 eyes) and group B (≥ 25%, 40 eyes). Pentacam was used to measure the posterior corneal elevation at the central point, thinnest point, and posterior maximum elevation (PME) and the mean posterior elevation in the central 2-mm area (MPE-2 mm), 4-mm area, and 6-mm area at the 3-year follow-up.ResultsMore than 85% of the eyes had an AR of less than 27%, and no cases of iatrogenic keratectasia developed. In both groups, for central region, posterior elevation decreased implying backward displacement; for peripheral region, it increased indicating forward trend. There was no significant difference in changes in all determined parameters between the two groups (P ≥ 0.07). Moreover, no significant correlation was noted between AR and posterior elevation changes. In group A, decreasing changes in PME (r = − 0.42, P = 0.01) and MPE-2 mm (r = 0.40, P = 0.01) demonstrated negative correlations with residual bed thickness.ConclusionRegion-dependent changes were demonstrated in the eyes that underwent SMILE. The central area showed a subtly declining posterior elevation, and the peripheral area showed a slightly increasing elevation. The limited ablation ratio had no impact on the changes in posterior corneal elevation.

Accelerated corneal collagen cross-linking in progressive keratoconus: Five-year results and predictors of visual and topographic outcomes.

To analyze the 5-year results of accelerated corneal collagen crosslinking (CXL) for progressive keratoconus and identify preoperative characteristics predictive of visual and topographic outcomes. A prospective interventional case series. Nineteen eyes of 19 patients receiving accelerated CXL with settings of 18 mW/cm2 for 5 min were included. Clinical and topographic parameters were assessed. Linear regression and logistic regression were used to compare the R2 and odds ratio (OR), respectively, between baseline characteristics and postoperative outcomes. Corrected distance visual acuity (CDVA) remained stable from 0.28 ± 0.21 to 0.25 ± 0.18 logMAR (P = 0.486). The mean cylindrical refraction was stable (P = 0.119). The maximal keratometry (Kmax) decreased from 61.99 ± 10.37 to 59.25 ± 7.75 D (P < 0.001), flattening in the flattest and steepest meridians and mean keratometry were also observed (P ≤ 0.040). The mean anterior elevation at the apex reduced from 21.42 ± 16.69 to 18.53 ± 12.74 μm (P = 0.013) and changes in posterior elevation were non-significant (P = 0.629). Preoperative Kmax best predicted the postoperative change in Kmax (R2 = 0.55, P < 0.001) compared to the other baseline characteristics (P ≤ 0.028), whereas preoperative CDVA was the only significant predictor of postoperative change in CDVA (R2 = 0.41, P = 0.003). Accelerated CXL is less likely to fail in eyes with a steeper preoperative Kmax (OR = 0.74, P = 0.040) or greater posterior elevation at the apex (OR = 0.91, P = 0.042). Kmax significantly decreased following accelerated CXL. Eyes with worse preoperative CDVA and higher Kmax were more likely to have an improvement in visual acuity and corneal flattening.

Corneal elevation changes after forced eyelid closure in healthy participants and in patients with keratoconus

BackgroundTo assess pointwise corneal elevation changes after forced eyelid closure test (FECT) in the eyes of healthy subjects and in eyes with keratoconus.MethodsTwenty‐nine subjects with keratoconus and 31 healthy volunteers were evaluated. Patients with keratoconus who had corneal hydrops, apical scarring, corneal thickness ≤ 400 μm, ocular surface disease, contact lens wear on the examination day and a history of corneal cross‐linking were excluded. Exclusion criteria for healthy participants were spherical error > +3.00 D and < −3.00 D, corneal astigmatism > 1.50 D, corneal curvature > 47 D, ocular allergy, clinical findings and family history of keratoconus. Pentacam was performed before and after 20-seconds of FECT and raw data were extracted from the built‐in software. Pointwise anterior and posterior elevation changes in the central 8-mm cornea were assessed using paired samples t‐test and heat maps were constructed to reflect mean changes and statistically significant data points. Statistical significance was assumed at p < 0.01.ResultsAge and gender were similar between healthy subjects (24.5 ± 1.6-years, 46.4 per cent female) and subjects with keratoconus (28.6 ± 9.2-years, 46.4 per cent female, p = 0.19, 0.61, respectively). Healthy eyes displayed posterior depression clustering in the inferotemporal and inferonasal areas (mean change: −4.5 ± 7.8 μm and −5.2 ± 9.8 μm, respectively, all p < 0.01). In contrast, keratoconus eyes exhibited a wider area of posterior elevation clustering in the inferior cornea (mean change: 8.1 ± 14.5 μm, all p < 0.01) with a small extension in the inferotemporal cornea (mean change: 12.1 ± 22.3 μm, all p < 0.01).ConclusionFECT elicits corneal elevation changes mainly in the inferior cornea with the change being more pronounced and wider in eyes with keratoconus.

Elevation Changes of Central Posterior Corneal Surface After Intracorneal Ring Segment Implantation in Keratoconus

To compare changes that occur at the posterior corneal surface after the implantation of intracorneal ring segments (ICRSs) using either mechanical or femtosecond laser-assisted procedures and to correlate these changes with the visual outcome achieved. Retrospective, nonrandomized, and interventional case series including 223 consecutive eyes of 186 patients with keratoconus ranging in age from 16 to 39 years that were implanted with ring segments (KeraRing; Mediphacos) at Kartal Training and Research Hospital, Istanbul, Turkey. Two groups were created according to the surgical technique used: mechanical group (168 eyes) and femtosecond group (55 eyes). Visual and refractive outcomes and corneal elevation changes were evaluated during a 24-month follow-up. Correlations between visual and posterior elevation changes were evaluated. The posterior corneal surface could not be analyzed with accuracy for diameters larger than the diameter of the ICRS implant. A statistically significant reduction of maximum elevation for both the corneal surfaces was observed at 1 month after the surgery (P < 0.01), with additional reductions at 3 and 6 months (P ≤ 0.03). In addition, the posterior best-fit sphere was flattened significantly at 1 month after the surgery in both the groups, with additional flattening at 3 months (P ≤ 0.03). No significant differences between groups in posterior corneal elevation parameters were found at any time point of the follow-up (P ≥ 0.14). Moderate and significant correlations of the postoperative visual outcome with the change in posterior best-fit sphere were found only in the femtosecond group. A central corneal flattening of the posterior corneal surface occurs after ring segment implantation in keratoconus.

Tomographic Normal Values for Corneal Elevation and Pachymetry in a Hyperopic Population

Purpose: To establish a normative data base with respect to corneal pachymetry and elevation tomography appropriate for refractive surgery screening of hyperopic individuals. Methods: 100 eyes of 51 consecutive hyperopic patients were examined with the Oculus Pentacam HR to determine corneal pachymetry and anterior and posterior elevation values at the apex and thinnest point. All patients were otherwise screened as normal and all principal meridians were hyperopic. Results were compared to a previously studied data base of myopic individuals from the same practice. Results: The average corneal thickness at the apex and thinnest point was not significantly different between the hyperopic and myopic groups (P>0.05 at both locations). The mean anterior elevation at the apex was0.4 ± 1.9 µm in the hyperopic group vs. 1.6 ± 1.3 µm in the myopic group (P<0.001). The mean anterior elevation at the thinnest point was-0.1 ± 2.2 µm in the hyperopic group vs. 1.7 ± 2.0 µm in the myopic group (P<0.001). The mean posterior elevation at the apex was5.7 ± 3.6 µm in the hyperopic group vs. 0.8 ± 3.0 µm in the myopic group (P<0.001). The mean posterior elevation at the thinnest point was10.6 ± 5.7 µm for the hyperopic group vs. 3.6 ± 4.1 µm for the myopic group (P<0.001). When adjusted for age, the posterior elevation changes remained statistically significant. Conclusions: Hyperopic individuals exhibited greater variation in posterior tomographic elevation values than a comparable myopic group. Currently used data bases need to be adjusted for screening hyperopic individuals to reduce the number of false positives associated with using a myopic biased data set.

Posterior Corneal Elevation After LASIK with Three Flap Techniques as Measured by Pentacam

To evaluate and compare posterior corneal changes using elevation data obtained from Pentacam (Oculus Optikgeräte GmbH) Scheimpflug imaging in eyes undergoing LASIK with three different modes of flap creation: IntraLase femtosecond laser FS60 (Abbott Medical Optics) (femtosecond group), Amadeus (Ziemer Group AG) mechanical microkeratome (keratome group), or flap formation using 20% alcohol laser epithelial keratomileusis (LASEK) (LASEK group). Ninety myopic patients (90 eyes) undergoing refractive surgery were recruited. The change in posterior corneal elevation at 21 predetermined points in the central 5-mm area was measured using exported elevation data from the Pentacam before LASIK and 18 months postoperative and was compared among and within three modes of flap creation. Mean change in posterior elevation in the central 5-mm area was 5.13±4.16 μm for the femtosecond group, 5.78±4.42 μm for the keratome group, and 6.68±4.72 μm for the LASEK group and was similar among groups (P=.59). Change in posterior elevation before and after LASIK was not significant within any group (P=.342, P=.232, and P=.321 for the femtosecond, keratome, and LASEK groups, respectively). Preoperative spherical equivalent, central corneal thickness, ablation depth, and estimated residual bed thickness did not correlate with change in posterior corneal elevation for the femtosecond, keratome, or LASEK groups (P>.05). Using Pentacam elevation data, there were no significant changes in posterior corneal elevation following LASIK among or within the three methods of flap creation. At 18 months after LASIK, the posterior corneal surface is not displaced anteriorly significantly and is equally stable using these three surgical techniques.

Long-term stability of the posterior cornea after laser in situ keratomileusis

To study long-term changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) using Scheimpflug topography (Pentacam, Oculus, Inc.) in eyes 1 year after LASIK. Department of Ophthalmology, Albany Medical Center, and a private practice, Albany, New York, USA. One hundred two myopic eyes of 52 consecutive patients presenting for their 1-year follow-up were prospectively evaluated using the Pentacam to determine elevation changes to the posterior corneal surface between preoperative and 1-year postoperative measurements. Changes in posterior elevation were performed by comparing the best-fit sphere preoperatively and postoperatively with a fixed reference sphere determined by the central 9.0 mm preoperative cornea. Statistical and graphical analyses were performed. One hundred two post-LASIK eyes (mean correction -4.33 diopters; mean ablation depth 68.70 microm; mean estimated residual bed thickness 327 microm) had a mean posterior displacement of -0.47 microm +/- 3.48 (SD) (range -10.0 to +7 microm). The mean follow-up period was 13.6 months (range 8.8 to 19.3 months). In this population, no patient had significant forward protrusion of the posterior corneal surface a mean of 14 months after LASIK. The posterior cornea in post-LASIK myopic eyes was very stable. Contrary to results in previous studies, progressive changes to the posterior corneal surface did not routinely occur after LASIK performed within established parameters.

Changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy

To study the changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using Scheimpflug topography with the Pentacam anterior segment imaging system (Oculus, Inc.). Department of Ophthalmology, Albany Medical Center, and a private clinical practice, Albany, New York, USA. In this prospective study, 121 consecutive myopic eyes (103 LASIK and 18 PRK) were evaluated preoperatively and postoperatively with the Pentacam to determine elevation changes in the posterior corneal surface. Changes in posterior elevation were calculated by comparing the best-fit sphere preoperatively and postoperatively to a fixed reference sphere using the central 9.0 mm preoperative cornea. Statistical and graphic analyses were performed. The 103 LASIK eyes had a mean correction of -3.76 diopters (D) and a mean ablation depth of 62.1 microm. The mean estimated residual bed thickness (RBT) (329 microm) demonstrated a mean posterior displacement of 2.64 +/- 4.95 microm. The 18 PRK eyes had a mean correction of -2.69 D and a mean ablation depth of 53.2 microm. The mean estimated RBT (464 microm) had a mean posterior displacement of -0.88 +/- 4.64 microm. The difference in the mean posterior corneal displacement between the LASIK and the PRK eyes was not statistically significant (P>.05, Student t test). There was no statistically significant difference in posterior corneal displacement between the LASIK and PRK patients. The changes in PRK and LASIK eyes appeared to be within acceptable measurement variation. Contrary to previous reports, ectatic changes to the posterior corneal surface did not routinely occur after LASIK surgery.